Optical pick-up device with a multifunctional prism

Abstract

The present invention provides an optical pickup device which enables cost reduction and has improved optical characteristics. In the optical pickup device according to the present invention, as a function to shape a light flux outputted from a semiconductor laser chip to a substantially circular beam and a function to separate reflected light from an optical recording medium from the source light are realized with one optical element, a number of required parts can be reduced, which in turn enables substantial cost reduction as well as size reduction of the device.

What is claimed is: 
     
       1. An optical pickup device, which comprises: a light source having a light flux output of non-circular cross-section;   a multi-functional single body prism in optical alignment with said light source;   at least one light directing optical member configured to focus light received from said multi-functional prism onto a optical recording medium and to direct light reflected from said optical recording medium to said multi-functional prism; and   a light detection system aligned with said multi-functional prism and configured to receive light reflected by said optical recording medium;   wherein said multi-functional prism has at least one face configured to shape said light flux outputted from said light source to a substantially circular beam, to direct said beam to said at least one light directing member, to separate light reflected from said optical recording medium from said source light, and to guide said reflected light separated from said source light to said light detection system; and   wherein a following expression is established in said multi-functional prism, such that an incidence angle of said light flux outputted from said semiconductor laser chip light source is a, and an angle between an incidence face of said multi-functional prism for said light flux and a first outgoing irradiation face of said multi-functional prism for said light flux subjected to beam shaping is α, an angle between said incidence face and a second outgoing irradiation face of said multi-functional prism from which said light flux subjected to light separation guided from said multi-functional prism is β, and an index of refraction of a material for said multi-functional prism is n:   
     
     
       2. An optical pickup device according to claim 1, wherein said multi-functional prism has a right-angled isosceles triangular form and a face corresponding to a bottom edge of a bottom edge thereof functions as a face for beam shaping as well as that for light separation. 
     
     
       3. An optical pickup device according to claim 1, wherein said multi-functional prism has a face which functions as a face for beam shaping as well as that for light separation on a same face and of said side faces a face from which a light flux subjected to beam shaping goes out and a face from which a light flux subjected to light separation goes out are set at an angle other than a right angle to an optical axis respectively. 
     
     
       4. An optical pickup device according to claim 1, wherein said at least one face of said multi-functional prism comprises a single face for directing light to said at least one light directing member and for separating said source light from said reflected light. 
     
     
       5. An optical pickup device according to claim 4, wherein in said multi-functional prism, an incidence angle of said light flux outputted from said light source is a, an angle between said incidence angle of said light flux and an outgoing irradiation face of said multi-functional prism from which said light flux is directed to said at least one light directing member is α, and an index of refraction of material for said multi-functional prism is n, and a relationship among a, α and n is expressed by the following expression. ##EQU4## 
     
     
       6. An optical pickup device, which comprises: a laser light source having a light flux output of non-circular cross-section;   a multi-functional single body prism in optical alignment with said light source;   at least one light directing optical member configured to focus light received from said multi-functional prism onto a optical recording medium and to direct light reflected from said optical recording medium to said multi-functional prism; and   a light detection system aligned with said multi-functional prism and configured to receive light reflected by said optical recording medium;   wherein said multi-functional prism has at least one face configured to shape said light flux outputted from said laser light source to a substantially circular beam, to direct said beam to said at least one light directing member, to separate light reflected from said optical recording medium from said source light, and to guide said reflected light separated from said source light to said light detection system, wherein said multifunctional prism includes:   a first wedge-shaped prism to shape said beam light flux; and   a second wedge-shaped prism assembled with and joined to said first wedge-shaped prism, wherein a junction face between said first wedge-shaped prism and said second wedge-shaped prism functions as a face for light separation;   wherein said first wedge-shaped prism and said second wedge-shaped prism have the same form and a slat face of said first wedge-shaped prism is jointed to that of said second wedge-shaped prism to form a pair of parallel planes; and   wherein an incidence angle of light flux coming into said first wedge-shaped prism is "a", an index of refraction of said first wedge-shaped prism is "n", and a vertical angle of said first wedge-shaped prism is "x", and a relation among "a", "n" and "x" is expressed by the following expression: ##EQU5##   
     
     
       7. An optical pickup device, which comprises: a laser light source having a light flux output of non-circular cross-section;   a multi-functional single body prism in optical alignment with said light source;   at least one light directing optical member configured to focus light received from said multi-functional prism onto a optical recording medium and to direct light reflected from said optical recording medium to said multi-functional prism; and   a light detection system aligned with said multi-functional prism and configured to receive light reflected by said optical recording medium;   wherein said multi-functional prism has at least one face configured to shape said light flux outputted from said laser light source to a substantially circular beam, to direct said beam to said at least one light directing member, to separate light reflected from said optical recording medium from said source light, and to guide said reflected light separated from said source light to said light detection system, and wherein in said multi-functional prism a first outgoing irradiation face from which said light flux subjected to beam shaping goes out to a light detection system does not cross an optical axis of said outgoing light flux and at said same time said optical axis of said light flux passing through said first outgoing irradiation face of said multi-functional prism crosses the optical axis of said light flux passing through a second outgoing irradiation face in a side of said light detection system at right angles.   
     
     
       8. An optical pickup device, which comprises: a laser light source having a light flux output of non-circular cross-section;   a multi-functional single body prism in optical alignment with said light source;   at least one light directing optical member configured to focus light received from said multi-functional prism onto a optical recording medium and to direct light reflected from said optical recording medium to said multi-functional prism; and   a light detection system aligned with said multi-functional prism and configured to receive light reflected by said optical recording medium;   wherein said multi-functional prism has at least one face configured to shape said light flux outputted from said laser light source to a substantially circular beam, to direct said beam to said at least one light directing member, to separate light reflected from said optical recording medium from said source light, and to guide said reflected light separated from said source light to said light detection system, and wherein a 1/4 wavelength plate is monolithically attached to a face of said multi-functional prism from which said light flux goes out to said optical recording medium.   
     
     
       9. An optical pickup device, which comprises: a laser light source having a light flux output of non-circular cross-section;   a multi-functional single body prism in optical alignment with said light source;   at least one light directing optical member configured to focus light received from said multi-functional prism onto a optical recording medium and to direct light reflected from said optical recording medium to said multi-functional prism; and   a light detection system aligned with said multi-functional prism and configured to receive light reflected by said optical recording medium;   wherein said multi-functional prism has at least one face configured to shape said light flux outputted from said laser light source to a substantially circular beam, to direct said beam to said at least one light directing member, to separate light reflected from said optical recording medium from said source light, and to guide said reflected light separated from said source light to said light detection system, and wherein in said multi-functional prism a first outgoing irradiation face from which said light flux subjected to beam shaping goes out to a side of an optical recording medium does not cross an optical axis of said outgoing light flux at right angles, an angle between said optical axis of said light flux passing through said first outgoing irradiation face of said multi-functional prism and said optical axis of said light flux passing through a second outgoing irradiation face of said multi-functional prism to said side of light detection system is a right angle, and a 1/4 wavelength plate is monolithically attached to a face from which said light flux goes out to said side of said optical recording medium.   
     
     
       10. An optical pickup device, which comprises: a laser light source having a light flux output of non-circular cross-section;   a multi-functional single body prism in optical alignment with said light source;   at least one light directing optical member configured to focus light received from said multi-functional prism onto a optical recording medium and to direct light reflected from said optical recording medium to said multi-functional prism; and   a light detection system aligned with said multi-functional prism and configured to receive light reflected by said optical recording medium;   wherein said multi-functional prism has at least one face configured to shape said light flux outputted from said laser light source to a substantially circular beam, to direct said beam to said at least one light directing member, to separate light reflected from said optical recording medium from said source light, and to guide said reflected light separated from said source light to said light detection system, and wherein in said multi-functional prism an outgoing irradiation from which said light flux subjected to beam shaping goes out to said optical recording medium does not cross an optical axis of said outgoing light flux, and a 1/2 wavelength plate is monolithically attached to a face from which said light flux goes out to said light detection system.   
     
     
       11. An optical pickup device, which comprises: a laser light source having a light flux output of non-circular cross-section;   a multi-functional single body prism in optical alignment with said light source;   at least one light directing optical member configured to focus light received from said multi-functional prism onto a optical recording medium and to direct light reflected from said optical recording medium to said multi-functional prism; and   a light detection system aligned with said multi-functional prism and configured to receive light reflected by said optical recording medium;   wherein said multi-functional prism has at least one face configured to shape said light flux outputted from said laser light source to a substantially circular beam, to direct said beam to said at least one light directing member, to separate light reflected from said optical recording medium from said source light, and to guide said reflected light separated from said source light to said light detection system, and wherein in said multi-functional prism a first outgoing irradiation face from which said light flux subjected to beam shaping goes out to said optical recording medium does not cross an optical axis of said outgoing light flux, an angle between said optical axis of said light flux passing through said first outgoing irradiation face of said multi-functional prism and said optical axis of said light flux passing through a second outgoing irradiation face of said multi-functional prism in a side of said light detection system is a right angle, and a 1/2 wavelength plate is monolithically attached to said face from which said light flux goes out to said light detection system.